var wrap = document.getElementById("wrap");
var main = document.getElementById("main");
var hei = document.body.clientHeight;
wrap.style.height = hei + "px";
var obj = document.getElementsByTagName("div");
for(var i=0;i<obj.length;i++){
    if(obj[i].className == 'page'){
        obj[i].style.height = hei + "px";
    }
}
//如果不加时间控制，滚动会过度灵敏，一次翻好几屏
var startTime = 0, //翻屏起始时间
    endTime = 0,
    now = 0;
//浏览器兼容
if ((navigator.userAgent.toLowerCase().indexOf("firefox")!=-1)){
    document.addEventListener("DOMMouseScroll",scrollFun,false);
}
else if (document.addEventListener) {
    document.addEventListener("mousewheel",scrollFun,false);
}
else if (document.attachEvent) {
    document.attachEvent("onmousewheel",scrollFun);
}
else{
    document.onmousewheel = scrollFun;
}
//滚动事件处理函数
function scrollFun(event){
    startTime = new Date().getTime();
    var delta = event.detail || (-event.wheelDelta);
//mousewheel事件中的 “event.wheelDelta” 属性值：返回的如果是正值说明滚轮是向上滚动
//DOMMouseScroll事件中的 “event.detail” 属性值：返回的如果是负值说明滚轮是向上滚动
    if ((endTime - startTime) < -1000){
        if(delta>0 && parseInt(main.offsetTop) > -(hei*5)){
//向下滚动
            now = now - hei;
            toPage(now);
        }
        if(delta<0 && parseInt(main.offsetTop) < 0){
//向上滚动
            now = now + hei;
            toPage(now);
        }
        endTime = new Date().getTime();
    }
    else{
        event.preventDefault();
    }
}
function toPage(now){
    $("#main").animate({top:(now+'px')},1000);     //jquery实现动画效果
//setTimeout("main.style.top = now + 'px'",1000);     javascript 实现动画效果
}